Triacylglycerols, which are storage lipids, are produced by the transfer of acyl moieties on diacylglycerols. Enzymes that transfer an acyl group to a diacylglycerol are called diacylglycerol acyltransferases (DGATs), and there are known an acyl-CoA:diacylglycerol acyltransferase (EC 2.3.1.20) of a type where acyl CoA serves an acyl donor and a phospholipid:diacylglycerol acyltransferase:PDAT (EC 2.3.1.158) of a type where a phospholipid serves an acyl donor.
DGAT which uses acyl CoA as an acyl donor is classified into 2 families of DGAT1 and DGAT2 due to differences in primary structure (Non-Patent Documents 1 and 2). Also, PDAT genes are cloned from yeast, plants, etc. (Patent Document 1 and Non-Patent Documents 3 and 4). Among them, it is known that PDAT derived from Arabidopsis utilizes as an acyl donor various phospholipids including phosphatidic acid, phosphatidylcholine, phosphatidylethanolamine, etc. and can transfer acyl residues ranging from C10-C22 (Non-Patent Document 5).
In the yeast Saccharomyces cerevisiae in which studies are relatively advanced in fungi, DGA1 (YOR245C) belonging to the DGAT2 family (Non-Patent Document 6) and LRO1 (YNR008W) which is PDAT are known as DGAT-encoding genes. The enzyme which is encoded by these two genes accounts for a large part of the DGAT activity in the yeast but even when these genes are simultaneously disrupted, the DGAT activity is not completely lost. It is known that the DGAT activity of the enzyme encoded by the ARE1 and ARE2 genes, which are acyl CoA:sterol acyltransferase genes, contributes to this remaining DGAT activity (Non-Patent Document 7).
With respect to Mortierella alpina (M. alpina), which is a lipid-producing fungus, 4 types of DGATs and their genes which utilize acyl CoA as an acyl donor are reported (two types of DGAT1 family genes and two types of DGAT2 family genes) (Patent Documents 2 and 3 and Non-Patent Document 8).
However, homologs of PDAT which uses a phospholipid as an acyl donor are unknown in M. alpina. A Δ5 fatty acid desaturase is an enzyme which catalyzes the oxidation of dihomo-γ-linolenic acid (DGLA) to form arachidonic acid (ARA). It is known in M. alpina that since the enzyme acts mainly on DGLA present as the acyl residues of phosphatidylcholine, arachidonic acid is formed as the acyl residues of phosphatidylcholine (Non-Patent Document 9). Therefore, enzymes for the synthesis of arachidonic acid-containing triacylglycerols from arachidonic acid present as the acyl residues of phospholipids such as phosphatidylcholine, etc. are required to promote the formation of triacylglycerols containing arachidonic acid.